Japanese Patent Application Laid-Open Publication No. 2004-130842 (hereinafter referred to as “Patent Literature 1”) discloses, as a vehicle collision determination device, an airbag control section, which includes a leftward/rightward acceleration sensor, a forward/backward acceleration sensor and a CPU. Further, in FIG. 3 of Patent Literature 1, the leftward/rightward acceleration sensor and the forward/backward acceleration sensor incorporated in the airbag control section are disposed in a central section or a passenger compartment of an automobile. Output of a combination of leftward/rightward acceleration sensor and the forward/backward acceleration sensor, which is to be used by the CPU for determining whether there has occurred frontal collision (front-surface type front collision) where the front surface or front bumper face of the automobile collides with another automobile, is provided as two-axis or biaxial output. Thus, the airbag control section can determine a form or mode of frontal collision.
More specifically, FIG. 10 of Patent Literature 1 shows a deployment control map (i.e., collision-mode determining two-dimensional map), and paragraph [0048] of Patent Literature 1 discloses that the airbag control section determines a mode of frontal collision to be asymmetric frontal collision if coordinates determined by a forward/backward total integrated value obtained by integrating the output of the forward/backward acceleration sensor and a leftward/rightward sectional integrated value obtained by sectionally integrating the output of the leftward-rightward acceleration sensor fall within a predetermined region (hatched region) in FIG. 10. In Patent Literature 1, the term “asymmetric frontal collision” embraces “automobile-to-automobile offset frontal collision” and “automobile-to-automobile oblique frontal collision” (i.e., automobile-to-automobile frontal collision where a portion (e.g., left portion) of the front surface of the automobile collides with a portion (e.g., left portion) of the front surface of another automobile).
In the case where the mode of the frontal collision is the asymmetric frontal collision, the above-mentioned airbag control section selects, for example, a low map deployment region from deployment regions (i.e., airbag-deployment-timing determining two-dimensional map) and outputs a deployment instruction for deploying frontal collision airbags (i.e., airbags for driver's and assistant driver's seats) when coordinates determined by the forward/backward total integrated value and a forward/backward sectional integrated value obtained by sectionally integrating the output of the forward/backward acceleration sensor fall within the selected low map portion.
Alternatively, until the coordinates determined by the forward/backward total integrated value and the leftward/rightward sectional integrated value fall within the above-mentioned hatched region, the airbag control section determines that the mode of the frontal collision is not the asymmetric frontal collision, i.e. that a symmetric frontal collision could occur. Here, the term “symmetric frontal collision” embraces “automobile-to-automobile full-wrap frontal collision” (i.e., automobile-to-automobile frontal collision where the entire front surface of the automobile collides with the entire front surface of another automobile) shown in (1-1) of FIG. 10. The airbag control section selects, for example, a high map deployment region from among the above-mentioned deployment regions, and when the coordinates determined by the forward/backward total integrated value and the forward/backward sectional integrated value fall within the high map deployment region, the airbag control section determines that the mode of the frontal collision is the symmetric frontal collision and outputs a deployment instruction for deploying the frontal collision airbags.
Namely, the airbag control section disclosed in Patent Literature 1 merely determines single timing for deploying the frontal collision airbags in accordance with the mode of the frontal collision. In other words, the airbag control section disclosed in Patent Literature 1 does not determine severity of the frontal collision. Further, although the airbag control section disclosed in Patent Literature can determine the “automobile-to-automobile offset frontal collision” and “automobile-to-automobile oblique frontal collision”, it cannot determine other modes of frontal collision, such as ODB (Offset Deformable Barrier) frontal collision where a part of the front surface of the automobile collides, for example, with a honeycomb structure provided on a concrete wall, and side-surface type front collision other than the front-surface type front collision. Here, the term “side-surface type front collision” embraces automobile-to-automobile intersecting side-surface type front collision where, for example, a front fender or engine room of the vehicle collides with a part of the front surface of another vehicle as the two vehicles enter an intersection.
The airbag control section disclosed in Patent Literature 1 or the deployment control map (collision-mode determining two-dimensional map) disclosed in FIG. 10 of Patent Literature 1 is an improvement of an airbag operating apparatus (vehicle collision determination apparatus) disclosed in FIG. 1 of Japanese Patent Application Laid-open Publication No. 2003-040077 (hereinafter referred to as “Patent Literature 2”) or a determining map (collision-mode determining two-dimensional map) disclosed in FIG. 3 of Patent Literature 2. According to paragraphs [0004] and [0005] of Patent Literature 2, the airbag operating apparatus (corresponding to the airbag control section in Patent Literature 1) includes electronic left and right sensors, in place of the mechanical left and right sensors (two forward/backward impact sensors) for detecting collision in the forward/backward direction in Patent Literature 1. Thus, the airbag operating apparatus disclosed in Patent Literature 2 or the airbag control section disclosed in Patent Literature 1 cannot determine severity of frontal collision, because severity of frontal collision is determined by use of output of mechanical left and right sensors as seen in an electronic control unit (vehicle collision determination device) or a severity determination section of FIG. 1 in Japanese Patent Application Laid-open Publication No. 2005-053341 (hereinafter referred to as “Patent Literature 3”).
FIG. 1 of Patent Literature 3 discloses electronic front sensors (two forward/backward acceleration sensors) provided in a front section of a vehicle, and FIG. 5 of Patent Literature 3 discloses a severity determining map or a floor deceleration reference value (one-dimensional threshold value). According to paragraphs [0039] and [0040] of Patent Literature 3, the severity determination section determines that severity is low if speed variation (namely, forward/backward sectional integrated value obtained by sectionally integrating output (deceleration) of an electronic floor sensor (forward/backward acceleration sensor) provided in a central section of the vehicle) exceeds the floor deceleration reference value before output of the front sensors exceeds a reference value (i.e., the front sensors are turned on) (see solid line in FIG. 5 of Patent Literature 3).
Further, FIG. 1 of Patent Literature 3 shows a multi (e.g., dual)-stage airbag having two inflators, and FIG. 6 of Patent Literature 3 shows a diagram (table) explanatory of delay times from first deployment timing for initially or first deploying the airbag to second deployment timing succeeding the first deployment timing. When severity of frontal collision is low, for example, the delay time is set at 30 ms. In other words, the airbag control section disclosed in Patent Literature 1 and the electronic control unit disclosed in Patent Literature 3, which cannot determine severity of frontal collision, cannot control a multi-stage airbag having a plurality of inflators.